This invention relates to metal-air electrochemical batteries and fuel cells particularly aluminum-air batteries suitable for electronic devices, including radio-telephones, portable audio and video players, video cameras, and personal computers.
There are known electrical rechargeable batteries comprising a housing with a pack of solid state cells, with a converter (controller) for stabilization of the output operating voltage when during the discharge cycle the voltage dips almost to one-half. In U.S. Pat. No. 5,656,876, a battery pack of lithium of NIxe2x80x94Cd solid-state cells is shown, where a DC/DC converter provides a stable operating voltage, possibly also different voltages upon request. U.S. Pat. No. 5,286,578 shows a flexible electrochemical cell having an air cathode, a metallic anode and an electrolyte chamber. The electrolyte chamber is collapsed when the battery is shipped (without electrolyte) to save space. U.S. Pat. No. 5,554,918 shows a mechanically rechargeable battery of a cylindrical shape having a replaceable zinc anode, an air electrode (one option) and housing. A non-spillable electrolyte is contained in the housing. When necessary, the anode can be removed and replaced with a new anode.
Batteries generally degrade during storage due to corrosion of the anode material. The corrosion results in one or more of the following, viz, loss of available energy in the cell, loss of cell voltage, and production of unwanted byproducts.
In order to decrease the corrosion of the anode material, a number of technologies are employed.
In one method, the addition of corrosion control inhibitors to the electrolyte is practiced. U.S. Pat. No. 5,378,559 teaches the addition of phosphate ester to the electrolyte of alkaline cells to reduce unwanted gas production at the anode. However, the addition of corrosion reducing chemicals adds to the cost of the cell and may adversely affect the power output of the cell.
A second approach known as water activation has been to keep the electrolyte separate from the cell until power is needed. U.S. Pat. No. 5,340,662 teaches an emergency battery with an infinite shelf life, wherein the primary battery is kept free of water until needed. U.S. Pat. No. 5,424,147 teaches a water activated battery with an aperture for aqueous liquid addition. U.S. Pat. No. 4,605,604 teaches a nickel-aluminum battery which has active components, but which has electrolyte stored separately. When power is needed the electrolyte must be transferred to the cell for activation. A disadvantage of these methods is that a liquid must be added to the cells before power can be produced. In all cases, additional external space and liquid handling capability must be available. Further, there is added complexity to the cell in order to allow transfer of the electrolyte to the cell and there is also the possibility of leakage due to the external connections for the filling of the electrolyte. Filling of a cell is usually difficult unless a second exit aperture is available to allow escape of the air displaced from the cell cavity.
A third approach has been to keep the electrolyte separate from one or both electrodes but within the cell compartment. The advantage is that no external electrolyte supply is needed. The key factor is that the ionic pathway is kept incomplete and the electrode(s) is kept isolated from the electrolyte. U.S. Pat. No. 3,653,972 teaches a cell in which the electrolyte is housed in a multiplicity of small capsules which keeps the electrolyte separate from the electrodes until the capsules are ruptured. However, the disadvantage of this arrangement is that multiple capsules must be broken and without breaking all of the capsules there will be loss of power due to unused electrolyte. There are also casings of the capsules that interfere with the ionic flow of chemical species in the cell and reduce the power output of the cell.
All of the above batteries suffer from a delay time before becoming active due to electrolyte filling and electrolyte wetting of the anode, cathode and membrane, if present. U.S. Pat. No. 6,136,468 teaches a similar concept of keeping the electrolyte separate from the electrodes by delaying full assembly of the cell until needed, while the electrolyte is immobilized in an adhesive protected by a release agent. Final assembly of the cell allows contact of the electrolyte with the electrodes. While this approach has application with electrolytes that can be immobilized in a gel type state, aqueous electrolytes would be difficult to handle. U.S. Pat. No. 4,059,717 teaches the use of a mask to inactivate a portion of the electrode and reduce corrosion of that masked area. Although battery life may be extended, there is still corrosion loss of the unprotected areas and a need to compensate for the loss in electrochemical activity caused by the mask. U.S. Pat. No. 5,314,502 teaches a electrically driven iontophoretic gate which when activated delivers ions to the cell and allows current to flow in the battery. The complexity of the cell, the electronics needed and the limited range of ions that can be delivered are limitations for this approach.
There is therefore a need for a metal-air battery which does not suffer from the aforesaid prior art disadvantages in providing extended shelf-storage life.
It is an object of the present invention to provide a metal-air battery having an extended pre-use shelf-storage life.
It is a further object of the present invention to provide such a battery for use, particularly, as a replaceable cartridge, within portable, hand-held cell phones, portable audio and visual players, cameras and the like, and personal computers.
The invention provides a metal-air battery having an extended shelf life by reason that the electrodes are not stored in contact with an electrolytic mixture, which mixture encourages corrosion of the anode until initial activation is desired, whereby the electrolyte is generated in situ to provide electrical contact between the anode and cathode. The battery is constituted in its simplest form as a self-contained cartridge adapted to be received by in electrical communication with, for example, a prior art DC/DC converter in the power receiving unit.
The cartridge is inexpensive and simple to manufacture. The battery with single or multiple anode, cathode and aqueous medium is constructed and sealed ready for use. The anode and cathode are pre-wetted ready for use and activates quickly. A surprising feature is that the battery shelf life is long in this wet state where anode and cathode are in contact with an anode non passivated surface-destroying aqueous medium. The prevention of corrosion is achieved by keeping the non passive film disrupting and film passive disrupting chemical species separated until desired by activation. The passive film disrupting species are contained in one embodiment in a rupturable device until needed in the cell for power production. A substantial reduction in cell complexity is achieved relative to the prior art. The passive disrupting species can be in dry form or concentrated aqueous form so that their in situ storage volume is minimal. The small quantity of passive film disrupting species allows for a small activating means and minimal interface with the operation of the cell. Unlike the cells which contain the electrolyte and have non conductive membranes or containment systems at least equal to the electrolyte volume and which are still present in the cell after rupture, the present invention has only a very small additive-containing chamber, which does not significantly interfere with power generation.
Accordingly, in one aspect the invention provides a battery comprising:
a consumable anode;
a gas-diffusion cathode;
a non passivated surfacexe2x80x94destroying aqueous medium in contact with the anode and cathode;
a housing enclosing the anode, cathode and medium;
an additive contained within a medium-impermeable chamber separated from but receivable by the medium upon activation to effect release from said chamber and mixing of the additive with the medium to provide an electrolytic mixture to effect electrical contact between the anode and cathode; and
activation means to effect said activation.
In one embodiment, the chamber is defined in part by a chamber wall formed of a puncturable material and the activation means comprises puncture means to effect puncture of the material upon activation. The puncturable material preferably is formed of a puncturable plastics material or metal in the form of a foil, skin or membrane.
In an alternative embodiment, the chamber is defined in part by a displaceable end wall sealing member and the activation means comprises displacing means to effect displacement of the sealing member to effect mixing of the additive and medium upon activation.
The displacing means further comprises biasing means to effect retraction of the sealing member after activation to effect sealing of the housing.
The anode is preferably formed of aluminum, zinc, magnesium or an alloy thereof.
Preferably, but not limiting, the gas-diffusion cathode comprises copper, more preferably, nickel-free copper i.e., for example, non-nickel-plated copper, in the form of a grid, screen mesh or the like, or bar, rod or plate. Copper alloys, such as for example, brass, may also be used.
A preferred additive comprises an alkali metal hydroxide, most preferably, potassium hydroxide, in the form of a powder, pellet or aqueous solution, which upon activation results in a potassium hydroxide concentration, preferably, of about 4 moles/litre.
By the term xe2x80x9cnon-passivated surface-destroying aqueous mediumxe2x80x9d in this specification and claims is meant a medium that, essentially, in the absence of the additive does not affect, i.e. corrode or de-passivate, the anode surface which is passivated by the presence of a metal oxide layer produced by contact with air or oxygen-containing aqueous media.
The preferred aqueous medium in the practice of the invention is de-ionized or distilled ion free-water. However anions, for example, stannate in association with potassium cations may be present, at say a concentration of 0.1-2% w/w.
The aqueous medium preferably has a pH within the range 4-12, most preferably, 5-9.
The medium may further comprise ingredients which cause the medium to be constituted as an aqueous, paste, or the like.